1. Field of the Invention
This invention relates to a gases supply and gases humidification apparatus, particularly, but not solely, for providing respiratory assistance to patients or users who require a supply of gas at positive pressure for the treatment of diseases such as Obstructive Sleep Apnea (OSA), snoring or Chronic Obstructive Pulmonary Disease (COPD) and the like. In particular, this invention relates to a humidifier chamber for use in a gases supply apparatus.
2. Summary of the Prior Art
A number of methods are known in the art for supplying humidified gases to a patient to assist a patient's breathing. Continuous Positive Airway Pressure (CPAP) involves the administration of air under pressure to a patient, usually by passing gases to the patient or user through a nasal mask. CPAP therapy is used in the treatment of snoring and Obstructive Sleep Apnoea (OSA), a condition characterised by repetitive collapse of the upper airway during inspiration. Positive pressure splints the upper airway open, preventing collapse. Treatment of OSA with CPAP has proven generally to be both effective and safe.
CPAP is also commonly used for patients with a variety of respiratory illnesses, including COPD (Chronic Obstructive Pulmonary Disease).
One of the side effects of CPAP therapy is that the stream of air can dry the nasal membranes, or the mouth and throat membranes of a user. This can lead to these areas becoming inflamed and uncomfortable. In order to counteract this side effect, it is usual for the air that is provided to a user to be humidified, by adding a humidification chamber or similar into the gases stream before the gas is provided to the patient. The gases enter the humidifier chamber, and are humidified as they pass over a volume of heated water contained in the chamber.
An ideal system is one that can deliver gas at the required pressure and temperature, with a maximum amount or maximum volume of water vapour contained in the gas. That is, gas at substantially 100% saturation or absolute humidity, delivered to a user at a relatively high temperature (the higher the temperature of the gas, the greater the volume of water vapour that it can contain). An ideal delivery temperature is one that is either the same as or slightly higher than the body temperature of the user.
Although systems exist that locate the humidifier close to the user, this arrangement tends to add weight close to the patient, and can increase their discomfort and decrease the usability of the system. Therefore, it is usual to locate the humidifier chamber remotely from the patient, with the heated humidified gases transported to the patient via a heated conduit.
A known (prior art) example of a system where the humidifier chamber is located remotely from the user is shown in FIG. 1. Gases are passed to the patient by way of a patient interface 2. In the system shown in FIG. 1, the interface 2 is a nasal cannula. However, full-face masks, nasal masks, nasal cannulas, oral mouthpieces, tracheostomy connections, or any other suitable interface can be used with these systems.
The cannula 2 is connected to a gases transportation pathway or inspiratory conduit 3 that in turn is connected to a humidifier chamber 5. A flow of gases is provided through the chamber 5 by an integrated blower unit contained within the housing 10.
Atmospheric air enters the housing 10 through an inlet 9 on the back of the casing 10, and is pressurised by a blower or fan assembly. The air is then passed into the humidification chamber 5 through an inlet 11. The humidification chamber 5 extends out from the housing 10 and can be removed and replaced by the patient or other user. The chamber 5 contains a volume of water that is heated via the base 13 of die chamber 5. The base 13 is heated by contact with an adjacent heated plate (not shown) that forms part of the system contained within the casing 10. The inspiratory conduit 3 is connected to the outlet 8 of the humidification chamber 5. It is usual for the walls of inspiratory conduit 3 to contain heating means or heater wires 7 that heat the walls of the conduit to reduce or eliminate the formation of condensation.
The gases supply and humidifying device contained within the housing 10 can be provided with a control means or an electronic controller such as a microprocessor that executes computer software commands stored in an associated memory. The user of the device may set a predetermined required value (preset value) of humidity or temperature of the gases supplied to patient 1, via a control interface such as a dial or buttons on a control pad or panel.
In response to the user set humidity or temperature value input, and other possible inputs such as system sensors that sense gases flow or temperature, the controller determines when (or to what level) to energise the heater plate. This in turn heats the volume of water 6 within humidification chamber 5 (via the conductive base 13). Water vapour fills the volume of the chamber above the surface of the water 6, rising from the surface of the water 6. Gases from the blower or fan pass into the chamber 5 through inlet 11 and become humidified as they pass across the top half of the chamber 5, that is, that part of the chamber 5 not filled with water 6.
The heated and humidified gas then passes out of the humidification chamber 5 via outlet 8 as fresh gases from the blower enter the chamber and displace the humidified, saturated gases.
The supply of gases through the inlet 11 is varied by a variable speed pump or fan 19 that draws air or other gases through the inlet 9. The speed of the variable speed pump or fan is preferably controlled by the control means or electronic controller described above.
Typically, humidification chambers such as chamber 5 are formed as a hollow shell with an open base. The shell is typically formed from a plastics material. A highly heat conductive metal plate 13 is added to close the open base, closing and sealing the chamber 5, except for the inlet 11 and outlet 8. In use, the base 13 is in direct contact with the heater plate. When the chamber 5 is in position substantially the entire surface area of the base 13 contacts the heater plate.
It should be noted that FIG. 1 merely illustrates one form of a suitable integrated gases supply and humidifying device. Other suitable gases supply systems, for example those that use fully separate or independent blowers and humidifiers connected in series, can also be used.
There are several disadvantages when using prior art systems of the type described above where the humidification chamber is located remotely from the patient. Some of these disadvantages are outlined below:                It is normally assumed that gases leaving the humidifier chamber are in a state of absolute humidity (100% saturated with water vapour). As described above, this saturated condition is desirable as it delivers a maximum amount of water vapour to the end user, and minimises any drying out of nasal or throat membranes. However, there is no guarantee that the gases leaving such humidifiers are in fact 100% saturated. This is because the saturation state of the gas leaving the chamber depends on a number of factors, including the temperature of the gas as it enters the chamber, the temperature of the water in the chamber, and the rate at which the gas passes through the chamber. Typically, humidification systems are only controlled to achieve a desired outlet gas temperature (not humidity).        Intermittent or varying flow rates (caused for example by fluctuating demand from the user's breathing) will cause the humidity of the gas passing out from the humidity chamber to be uneven. Air that passes through the humidifier at a high flow rate has had little time to be heated and humidified, while low flow rate gas lingers in the chamber longer, and therefore absorbs more water vapour, leaving the chamber at a higher absolute humidity. Varying flow rates caused by fluctuating user demand cause the flow rate of the gas through the chamber to vary at a greater rate than it is possible to compensate for using a control/feedback loop. It is not possible to compensate for varying flow rates by varying the inputs, e.g. varying heater power.        It is usual for humidifiers of the prior art type to be heated from the base. That is, the base of the humidifier chamber is made of a conducting material, with the volume of water in the chamber heated via this base. Air from the respirator or blower enters the chamber at or towards one side, above the level of the water within the chamber. The air passes over the heated water and becomes humidified, and then exits the chamber at the far side. This arrangement can be inefficient If air or gas enters the chamber at a lower temperature than the water and the saturated vapour in the chamber, it is likely that the gas will exit the chamber in a state where it is not fully saturated (not in a state of absolute humidity).        
In an attempt to overcome or minimise these difficulties, some prior art systems preheat gases before they enter the humidification chamber. However, these gases can lose heat energy as they travel from the pre-heater to the humidification chamber. It is usually not possible to retrofit a pre-heater in an existing blower unit. Therefore, in a gases supply and gases humidification system if a pre-heater is to be added, the blower unit most often needs to be replaced. This can be expensive.
U.S. Pat. No. 6,918,389 discloses a humidifier and sensor for use with a breathing assistance apparatus. A number of different configurations of humidification chambers are disclosed. Also disclosed are a number of methods and apparatus for heating the gases passing through the humidifier chambers. In particular, this patent discloses chambers that include an internal heating element such as a metal scroll element, a porous material element, or a semipermeable membrane. These elements provide both wet and dry heating of the gases passing through the chamber. This patent also discloses using heaters to preheat gases entering the chamber.
U.S. Pat. No. 4,753,758 discloses a respiratory humidifier with an internal partition wall, dividing the humidifier into a water reservoir and a humidification enclosure. The partition wall allows water vapour or humidified gas to pass through from the water reservoir to the humidification enclosure, but does not allow liquid water or water in droplet form to pass through. A second heater, having the form of a conical finned heater, can be located in the humidification enclosure to provide additional heating. The finned heater as described is centrally located and there is no direct heating of the gases passing through the inlet or outlet ports of the humidifier. The partition wall described includes a filter element. Several different alternative filter constructions are described. A certain amount of system pressure is required to force the water and gas through filters of this type.